Zero Magnetic Field Plateau Phase Transition in Higher Chern Number Quantum Anomalous Hall Insulators

TL;DR

This study demonstrates a zero magnetic field quantum phase transition between C=1 and C=2 quantum anomalous Hall states in magnetic topological insulator heterostructures, revealing coexistence of chiral edge channels and bulk conduction.

Contribution

It reports the first observation of a zero magnetic field topological phase transition between different Chern number QAH states using molecular beam epitaxy.

Findings

Monotonic decrease of Hall resistance from h/e2 to h/2e2 at transition

Maximum longitudinal resistance at the critical point

Coexistence of chiral edge channel and bulk conduction channels

Abstract

The plateau-to-plateau transition in quantum Hall effect under high magnetic fields is a celebrated quantum phase transition between two topological states through either sweeping the magnetic field or tuning the carrier density. The recent realization of the quantum anomalous Hall (QAH) insulators with tunable Chern numbers introduces the channel degree of freedom to the dissipation-free chiral edge transport and makes the study of the quantum phase transition between two topological states under zero magnetic field possible. Here, we synthesized the magnetic topological insulator (TI)/TI penta-layer heterostructures with different Cr doping concentrations in the middle magnetic TI layers using molecular beam epitaxy (MBE). By performing transport measurements, we found a zero magnetic field quantum phase transition between the C = 1 and C = 2 QAH states. In tuning the transition, the Hall resistance monotonically decreases from h/e2 to h/2e2, concurrently, the longitudinal resistance exhibits a maximum at the critical point. Our results show that the ratio between the Hall resistance and the longitudinal resistance is greater than 1 at the critical point, which indicates that the original chiral edge channel from the C = 1 QAH state coexists with the dissipative bulk conduction channels. Subsequently, these bulk conduction channels appear to self-organize and form the second chiral edge channel in completing the plateau phase transition. Our study will motivate further investigations of this novel Chern number change-induced quantum phase transition and advance the development of the QAH chiral edge current-based electronic and spintronic devices.